In manufacturing operations, "stamping" is a general terms that covers almost all press operations. It includes blanking, shearing, hot or cold forming, drawing, bending, and coining. Common among such operations is the objective of developing a less expensive method of producing sheet metal stampings, for example, of steel or aluminum. Especially in manufacturing "niche" or low volume vehicles, set up costs and down time must be minimized in order to produce efficient operations. Thus, it would be desirable to reduce the number of operations, particularly at production volumes of less than about 30,000 units per year from about seven steps to about three or four steps. Additionally, it would be desirable to eliminate tooling which is part-specific, so that once mounted, given tooling could be used to shape more than one part. Such manufacturing objectives are particularly important when one considers entry into a new vehicle market with minimum initial investment.
Thus, there has been a general interest in performing a large variety of small-lot production operations for automobile-related industries which conventionally specialize in mass production. In an era of diversification and personalization of the user's needs, there is a requirement for varied production of small lots to make it possible to meet the variously changing needs efficiently and accurately.
One such manufacturing system is the Toyota Flexible Press System (FPS). This system uses three basic operations per part (form/trim/finish) as compared with about 4-7 operations per part in conventional high volume stamping operations. In the Flexible Press System, a high variety, small volume production line exists for automobile body panels. The production line includes three processes: (1) hydraulic press forming; (2) high-speed three-dimensional carbon dioxide laser cutting; and (3) "multi-press" forming. However, the FPS uses relatively expensive return springs or compressed gas (e.g. nitrogen) cylinders to cause components to move within the die assembly.
In conventional stamping operations, there frequently is a-need for actuators that include a locking mechanism for holding a ram in an extended position. Illustrative is U.S. Pat. No. 4,951,552, which discloses a locking cylinder in which a locking ball is positioned within a ball passageway so that the balls do not project therefrom. Such mechanisms, however, do not readily lend themselves to low volume stamping operations. Nor do they disclose a structure which holds the ram during the initial stages of retraction. Additionally, it is doubtful that an invention disclosed in the '552 patent permits axial rotation of the shaft.